不同pH条件下河道底泥净化再生水试验研究

Experimental Study on Purification of Reclaimed Water by River Sediment under Different pH Conditions

北方城市景观河流的主要用水来自再生水,但其氮含量较高,有造成河流富营养化与地下水污染的风险。河道底泥作为河水与地下水间的介质,能够通过物理、化学和生物反应对水体起到净化作用,河道水环境酸碱条件对底泥NO_(3)^(-)-N净化效果有一定影响。通过河槽模拟装置,探究进水pH为4、7和10条件下河槽系统中底泥对NO_(3)^(-)-N的净化效果。结果表明:3种pH条件下河槽系统对NO_(3)^(-)-N均有显著净化作用,整体去除率分别为51.3%、57.5%和69.9%;尤其在河槽底泥10、20和30 cm处NO_(3)^(-)-N净化效果较好,去除率均在89.0%以上;在50和70 cm处3种pH处理之间NO_(3)^(-)-N去除率差异明显,在pH=4条件下去除效果较好;在NO_(3)^(-)-N浓度的垂向变化上,3种pH条件下底泥中NO_(3)^(-)-N浓度在10、20和30 cm处均较低,50和70 cm处较高。pH=4和10条件下底层水NH_(4)^(+)-N浓度高于pH=7条件下NH_(4)^(+)-N浓度,即酸碱条件下底泥对氨氮去除能力较差;NO_(3)^(-)-N在pH=7和10条件下试验前期与pH=4条件下试验中期产生累积,但最终实现对其的去除。在pH=7和10条件下底层水pH与NO_(3)^(-)-N浓度呈现显著负相关(P<0.05)。当进水pH分别为4、7和10时,底泥中pH仍然在7~9之间,说明水环境对外来酸碱变化有一定缓冲性,即具有抗酸、抗碱能力。该研究表明在不同酸碱条件下河道底泥对再生水具有净化作用,碱性条件下底泥对NO_(3)^(-)-N净化效果较好,中性条件下底泥对NH_(4)^(+)-N净化效果较好,可为北方再生水安全回补河湖提供参考。

Reclaimed water is the primary source of urban landscape rivers in northern China, but its high nitrogen content can lead to river eutrophication and groundwater contamination. However, river sediment is the medium between river water and groundwater, which can help to purify water through physical, chemical and biological reactions, and the acid-base conditions of river water environment have a certain impact on the purification effect of sediment NO_(3)^(-)-N. Using a river channel simulator, the aim of this experiment is to determine how well sediment in the trough system can remove NO_(3)^(-)-N from inlet water with pH levels of 4, 7, and 10, respectively. The results indicated that sediment in the trough system had a significant impact on the removal of NO_(3)^(-)-N under all the three pH conditions, with the overall removal efficiency being 51.3%, 57.5% and 69.9%, respectively. The impact is more pronounced at the depths of 10, 20 and 30 cm of trough sediment, where the removal efficiency of NO-N was higher than 89.0%. The removal efficiency differed considerably across the three pH treatments at 50 and 70 cm, with the best removal efficiency occurring at pH=4. In the vertical variation, ρ(NO_(3)^(-)-N) in the sediment was relatively lower at 10, 20 and 30 cm, and relatively higher at 50 and 70 cm under all three conditions. It was also observed that ρ(NH_(4)^(+)-N) of bottom water at pH values of 4 and 10, was higher than that with pH values of 7, indicating that the removal ability of sediment to ammonia nitrogen was poor under acid-base conditions. NO_(3)^(-)-N accumulated in the initial phase of pH=7 and 10 and the intermediate phase of pH=4, but it was finally eliminated. When pH=7 and 10, there was a significant negative correlation between bottom water pH and NO_(3)^(-)-N concentration(P< 0.05). When the pH of the influent was 4, 7 and 10, the pH of the sediment remained between 7 and 9, indicating that the water environment provided a certain buffer against external acid-base changes, i. e. it has the ability to resist acid and alkali. The study demonstrates the purification effects of riverbed sediment on reclaimed water under different acid-base conditions, the sediment under alkaline conditions has a better purification effect on NO_(3)^(-)-N, whereas the sediment under neutral conditions has a greater purification effect on NH_(4)^(+)-N. This information can be used as a reference for the safe recharge of reclaimed water to rivers and lakes.